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Temperature Water Potential Interactions on Growth and Sclerotial Germination of Phymatotrichum omnivorum. M. F. Stapper, Formerly technician, Texas Agricultural Experiment Station, Temple 76501; S. D. Lyda(2), and W. R. Jordan(3). (2)Plant pathologist, Texas Agricultural Experiment Station, College Station 77843; (3)Plant physiologist, Texas Agricultural Experiment Station, Temple 76501. Phytopathology 74:509-513. Accepted for publication 7 December 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-509.

The response of Phymatotrichum omnivorum to the osmotic and vapor transfer-controlled components of the soil water potential under different temperatures was investigated. Mycelial growth on potato-dextrose agar (PDA) declined as the osmotically controlled water potential decreased from - 4.5 to - 50 bars at 20 and 28 C. At 35 C, colony growth reached a maximum between - 8.5 and - 15 bars. Growth was more rapid at 35 C than at 28 C at water potentials <- 8 bars. Colony diameters at 20 C were less than those at 28 and 35 C at all water potentials. The use of sucrose instead of KCl to control water potential resulted in more growth and growth at lower water potentials. The three temperatures had a similar effect on the growth water potential curves, whether the water potential was controlled osmotically or by vapor transfer, but there was a change to lower values of the optimal and minimal matric potentials for growth. Sclerotia of P. omnivorum germinated rapidly in culture over a range of water potentials including those expected in dry soil (<- 10 bars). Germination percentages at 28 and 35 C were similar and higher than those at 20 C. Germination on PDA was greater and occurred at lower osmotic potentials than on water agar at all temperatures. Sclerotial germination responded similarly to osmotic- and vapor-transfer water potentials.

Additional keywords: culture media, thermocouple psychrometry.